Electroplating apparatus and method

ABSTRACT

Provided is an electroplating apparatus including: a water tank that is filled with a non-polar solvent having a higher specific gravity than an electrolyte in which an electrolyte layer is formed on top of the non-polar solvent; a copper electrode that is installed at a portion where the electrolyte layer of the water tank is positioned; an insulating substrate that is disposed to be inserted into and withdrawn from the water tank and on which seed electrodes are formed; an actuator that escalates the insulating substrate up and down; and a power supply that applies electric current between the copper electrode and each of the seed electrodes, to thereby uniformly form thickness of a metal thin film on a large substrate and guarantee grain size.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2011-065376, filed on Jul. 1, 2011 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for forming a metal thin film on a substrate, and more particularly, to an electroplating apparatus and method that can uniformly form a metal thin film on a large substrate.

2. Description of the Related Art

In general, various kinds of metal and metal alloys such as aluminum (Al), molybdenum (Mo), and molybdenum-tungsten (MoW) are used as a gate electrode constituting a bottom gate of a thin film transistor hereinafter referred to (TFT). The reason why the aluminum (Al), molybdenum (Mo), molybdenum-tungsten (MoW), etc., are used as a material of the gate electrode is because for example aluminum oxide (Al₂O₃) can be used as a gate insulation film to thereby make it easy to make the gate insulation film.

However, in the case that aluminum is used as a gate electrode material to implement a large display, in recent years, a resistance value of a gate line (GL) that is mutually connected with a gate electrode and is simultaneously formed with the gate electrode and that is simultaneously formed together with the gate electrode in general, or a data line (DL) that is orthogonally formed with respect to the gate line (GL) and is connected to a source region, is greatly increased in proportion to the dimension of a display. As a result, a gate signal and a data signal have been delayed and distorted.

In particular, in the case of an ultra-large flat-panel display whose one side is one meter or more long, a total length of wires increases exponentially. Accordingly, it is essential to use copper with low resistance as a material of wires. Since it is difficult to lower resistance of a gate wire of a thin film transistor (TFT) in comparison with that of a data wire, among the gate and data wires, it is required to use copper as the gate wire.

Conventional gate electrode materials are metal materials including copper (Cu) whose resistance is smaller than that of aluminum (Al). However, an appropriate etching solution that is used for etching a copper film in order to form the gate electrode and gate line has not been developed. Further, there is a problem that an etching process for etching the copper film produces heavy metals causing an environmental pollution.

Unlike the above-described metal and metal alloys, copper does not constitutes fluoride or chloride, there is a problem that copper is not well etched. In addition, in the case that copper is piled up with a thick thickness in order to reduce resistance, there is a problem that it takes 3-4 hours or longer as a processing time.

In addition, in the case that copper is used as the gate electrode in a large display, respective copper wires of two micrometers or more thick are required in order to make resistance of the copper wires sufficiently small. However, it takes long time to form a copper thick film of such a thickness. Further, in the case that a gate electrode structure of a thick film is employed, a gate insulation film that is directly formed on the upper portion of a gate electrode by a well-known process may cause a step coverage problem.

In order to these problems, a thick insulation film of two micrometers or so is deposited and patterned, to thereby form a trench structure. The trench structure is filled with copper by an electrodeposition process, to thus form wires. Here, a special technology is needed to selectively electrodeposite copper in the trench structure. According to the conventional electrodeposition technology, it is not possible to form a uniform copper film on the entire surface of the substrate because of high resistance in the case of a large area display. Besides, there is a need to use a large container accommodating a liquid electrolyte.

Meanwhile, a conventional technology of manufacturing an array substrate using copper as a gate electrode is disclosed in Korean Patent Laid-open Publication No. 10-2006-115522.

In the Korean Patent Laid-open Publication No. 10-2006-115522, signal wires and a thin film transistor are manufactured using an electroless plating method or an electroplating method whose deposition temperature is low, considering manufacturing temperature and stress act as big constraints in the case that the array substrate using copper as a gate electrode, in comparison with a case that a glass substrates is used at the time of production of signal wires such as gate lines and data lines and a thin film transistor in order to implement a flexible display device, to thereby prevent a flexible substrate from being bent or signal line layers from being cracked, and simultaneously to thereby promote a quality of display to be improved.

To this end, the Korean Patent Laid-open Publication No. 10-2006-115522 discloses that a first electrode layer made of nickel or molybdenum, a second electrode layer made of copper, and first and second line layers for use in gate lines and data lines are formed by the electroless plating method, to thereby form an electroplating seed layer, and then source and drain regions, and a third electrode layer and a third line layer for use in gate lines and data lines are formed by the electroplating method using the electroplating seed layer.

However, the method of forming the copper gate electrode and wires of the Korean Patent Laid-open Publication No. 10-2006-115522 includes a process of patterning first and second electrode layers so as to form the copper gate electrode and wires using the electroplating method, after having formed the first electrode layer for enhanced adhesion and the second electrode layer made of copper on the entire surface of the substrate by the electroless plating method. As a result, the Korean Patent Laid-open Publication No. 10-2006-115522 has the same problem as that of the conventional art at the time of etching the copper metal layer.

In addition, the technology disclosed in the Korean Patent Laid-open Publication No. 10-2006-115522 may cause a step coverage problem in a subsequent process because the gate electrode is formed as a thick film of one micrometer or more thick, and does not present any related solutions.

Moreover, when source and drain regions are formed in alignment with a gate electrode in the conventional art, a mask for shielding ion implantation is formed on the upper portion of the gate electrode by using a separate exposure mask and then an ion implantation process is executed. Accordingly, an alignment error of 2 to 4 micrometers may be caused. Further, such an alignment error cannot be equally distributed to both ends of a channel region and leans toward one end of the channel region, to thereby become a factor of aggravating an electrical performance of the thin film transistor (TFT).

Meanwhile, a copper electroplating process is a conventional technology, but has no problem when it is used in general with a traditional approach. However, in the case of a large substrate whose one side is two or more meters long, a problem such as a voltage drop may be caused. Accordingly, it is difficult to electroplate a metal film of uniform thickness on the large substrate.

In addition, the copper electroplating process requires that a container containing an electrolyte should be large in itself, and a huge amount of the electrolyte should be needed, to accordingly cause many industrial problems.

Moreover, when the electroplating is utilized in a semiconductor manufacturing process, a problem bigger than that of maintaining uniformity in thickness of an electrodeposited metal film is regulation of grain size. When grains are ripened as an example, the surface of the electrodeposited metal film becomes coarse. Thus, since surface roughness of a few micrometers may also cause a big problem in the semiconductor manufacturing process, grain size should become a micrometer level or less unlike typical applicable cases.

A conventional typical wet copper plating system is configured as shown in FIG. 1. In FIG. 1, a plate-shaped copper (Cu) electrode 160 and a substrate 130 on which a metal seed layer 150, that is, a metal electrode is formed in which copper plating is performed on the metal electrode are dipped in an electroplating tub 100 that is filled with a CuSO₄ electrolyte 110. Then, the metal seed layer that is the metal electrode 150 is established as a cathode and the copper electrode 160 is established as an anode. Then, electric power is supplied from a power supply 140 in order to execute an electroplating process. Accordingly, a copper plated layer 170 is electrodeposited on the metal seed layer that is the metal electrode 150.

Meanwhile, in the case of using the conventional typical wet copper plating system that dips a large-area substrate whose electrodeposition area is wide like a large display substrate whose one side is two meters or longer, in order to perform a copper plating process, the metal electrode 150 that is used as the cathode may cause a big difference in electric current densities between a portion “a” close to a power supply 140 and a portion “b” far from the power supply 140, due to a voltage drop across resistance values of the portions “a” and “b” as shown in FIG. 2.

During performing the wet copper plating process, an electrodeposition rate is proportional to an electric current density. Here, the following formula is established.

Electric current density=Electric current/Electrodeposition area

Thus, since copper (Cu) nucleation occurs rapidly at a portion of a high current density, grain size is small as illustrated as the portion “a” of FIG. 2. However, since nucleation does not occur well at a portion of a low current density, a phenomenon that grain size becomes large occurs as the portion “b” of FIG. 2.

In the electroplating process, grain size is dependent upon a voltage applied across both a cathode and an anode, an electric current that flows between the cathode and the anode, an electrolyte concentration, a distance between the cathode and the anode. Thus, in the case of using a large tub that can contain a large display substrate, it is extremely difficult to control such many variables.

As a result, in the case that copper plating is performed on a large-area substrate by using the conventional wet plating method employing the conventional dipping process, grain of a plated copper film is not formed into a uniform size.

SUMMARY OF THE INVENTION

To solve the above conventional problems or defects, it is an object of the present invention to provide an electroplating apparatus and method that can uniformly form thickness of a metal thin film on a large substrate, and that can guarantee grain size.

In addition, it is another object of the present invention to provide an electroplating apparatus and method that has no need to use a pattern forming process of forming metal wires having a low resistance value in order to avoid signal delay or distortion from occurring in a large-size display, to shorten a plating time and uniformly form thickness of a metal thin film.

The technical objects that are solved in the present invention are not limited to the above-described technical objects, and the other technical objects that have not been referred to can be clearly understood by one who has an ordinary skill in the art in the technical field to which the present invention belongs from the following description.

To accomplish the above and other objects of the present invention, according to an aspect of the present invention, there is provided an electroplating apparatus comprising:

a water tank that is filled with a non-polar solvent having a higher specific gravity than an electrolyte in which an electrolyte layer is formed on top of the non-polar solvent;

a copper electrode that is installed at a portion where the electrolyte layer of the water tank is positioned;

an insulating substrate that is disposed to be inserted into and withdrawn from the water tank and on which seed electrodes are formed;

an actuator that escalates the insulating substrate up and down; and

a power supply that applies electric current between the copper electrode and each of the seed electrodes.

Preferably but not necessarily, chloroform whose specific gravity is 1.5 g/ml is used as the non-polar solvent.

Preferably but not necessarily, a copper film is formed on the surface of each seed electrode, when the insulating substrate is inserted into the water tank.

According to another aspect of the present invention, there is also provided an electroplating apparatus comprising:

a water tank that is filled with a first non-polar solvent having a higher specific gravity than an electrolyte and a second non-polar solvent having a lower specific gravity than the electrolyte in which an electrolyte layer is formed between the first and second non-polar solvents;

a copper electrode that is installed at a portion where the electrolyte layer of the water tank is positioned;

an insulating substrate that is disposed to be escalated in the water tank and on which seed electrodes are formed;

an actuator that escalates the insulating substrate up and down; and

a power supply that applies electric current between the copper electrode and each of the seed electrodes.

Preferably but not necessarily, chloroform is used as the first non-polar solvent, and hexane is used as the second non-polar solvent.

Preferably but not necessarily, a copper film is formed on the surface of each seed electrode, when the insulating substrate is withdrawn from the water tank.

According to still another aspect of the present invention, there is also provided an electroplating method comprising the steps of:

filling a non-polar solvent whose specific gravity is higher than that of an electrolyte in a water tank and forming an electrolyte layer on top of the non-polar solvent;

installing a copper electrode at a portion where the electrolyte layer of the water tank is positioned;

inserting an insulating substrate on which seed electrodes are formed from the upper side of the water tank to the inside of the water tank at constant speed; and

applying electric current between each of the seed electrodes and the copper electrode to thus sequentially form a copper film on the surface of each seed electrode that passes through the electrolyte layer.

According to yet another aspect of the present invention, there is also provided an electroplating method comprising the steps of:

filling a first non-polar solvent whose specific gravity is higher than that of an electrolyte and a second non-polar solvent whose specific gravity is lower than that of the electrolyte in a water tank and forming an electrolyte layer between the first and second non-polar solvents;

installing a copper electrode at a portion where the electrolyte layer of the water tank is positioned;

withdrawing an insulating substrate on which seed electrodes are formed from the inside of the water tank to the upper side of the water tank at constant speed; and

applying electric current between each of the seed electrodes and the copper electrode to thus sequentially form a copper film on the surface of each seed electrode that passes through the electrolyte layer.

ADVANTAGEOUS EFFECTS

As described above, an electroplating apparatus and method according to the present invention can form a metal thin film uniformly in thickness on a large substrate, and guarantee grain size, in which a thin electrolyte layer is formed in the inside of a water tub and then an insulating substrate is made to escalate, to thereby sequentially make a copper film on seed electrodes, respectively.

In addition, the electroplating apparatus and method according to the present invention can form a copper film on a large substrate, to thereby have no need to use a pattern forming process of forming metal wires having a low resistance value in order to avoid signal delay or distortion from occurring in a large-size display, and to thus shorten a plating time and uniformly form thickness of a metal thin film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configurational diagram showing a conventional wet copper electroplating apparatus.

FIG. 2 shows photographs showing that grain size varies according to local areas when a copper film is formed on a large substrate using a wet copper electroplating apparatus according to the conventional art.

FIG. 3 is a perspective view showing an electroplating apparatus according to an embodiment of the present invention.

FIG. 4 is a perspective view showing an electroplating apparatus according to another embodiment of the present invention.

FIG. 5 is a plan view illustrating an array substrate of a liquid crystal display device according to the present invention.

FIGS. 6 through 21 are cross-sectional views illustrating a process of manufacturing a trench type copper bottom gate thin film transistor, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The above and/or other objects and/or advantages of the present invention will become more apparent by the following description.

Hereinbelow, an electroplating apparatus and method according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings FIGS. 3 through 22. Here, components shown in the drawings can be exaggerated in size or shape for illustrative clarity and convenience. In addition, terms that are specifically defined by considering configuration and function of the present invention may vary depending on a user's or operator's intention or practice. The definition of these terms should be made based on contents that are described through this disclosure.

FIG. 3 is a perspective view showing an electroplating apparatus according to an embodiment of the present invention.

Referring to FIG. 3, the electroplating apparatus according to the embodiment according to the present invention includes: a water tank 50 that is filled with a non-polar solvent 52 having a higher specific gravity than an electrolyte 54 in which an electrolyte layer 54 is formed on top of the non-polar solvent 52; a copper electrode 56 that is installed at an upper-inner end of the water tank 50; an insulating substrate 11 that is disposed to move up and down in the water tank 50 and on which seed electrodes 12 are formed, in which the insulating substrate 11 is inserted into the water tank 50; an actuator 64 that escalates the insulating substrate 11 up and down; and a power supply 62 that applies electric current between the copper electrode 56 and each of the seed electrodes 12.

The upper surface of the water tank 50 is opened to thereby make the insulating substrate 11 inserted into and withdrawn from the water tank 50 vertically through the opened upper surface. In addition, the water tank 50 is enough high to make the insulating substrate 11 inserted entirely into the water tank 50. Further, the water tank 52 is enough wide to make the insulating substrate 11 inserted entirely into the water tank 50. However, if the water tank 50 has a narrow width, the electrolyte or non-polar solvent 52 can be saved to thus prevent waste thereof.

A solvent whose specific gravity is higher than that of an electrolyte and that is not mixed with the electrolyte is used as the non-polar solvent 52 in order that the electrolyte layer 54 may be disposed on the upper surface of the non-polar solvent 52.

A copper sulfate aqueous solution may be preferably used as an electrolyte and chloroform whose specific gravity is 1.5 g/ml and that is a liquid that is nonflammable, transparent, fluent and high density may be preferably used as the non-polar solvent 52.

Therefore, the water tank 50 is filled with the non-polar solvent 52 and the electrolyte layer 54 is formed on the upper surface of the non-polar solvent 52. Since electrodeposition is performed only at a portion where the electrolyte layer 54 exists, thickness of the electrolyte layer 54 may be adjusted. Thus, if thickness of the electrolyte layer 54 is adjusted, length of the copper film that is electrodeposited at a time during electroplating can be controlled.

The electrolyte layer 54 is set in a thickness that the copper film can be electrodeposited with a uniform thickness on a large substrate through various experiments.

A sputtering or thin film deposition method may be used as a method of forming seed electrodes 12 on the insulating substrate 11. The method of forming seed electrodes 12 on the insulating substrate 11 will be described below in detail.

The copper electrode 56 is formed at an upper-inner end of the water tank 50, that is, at a portion where the electrolyte layer 54 is positioned, to then contact the electrolyte layer 54.

In addition, the power supply 62 plays a role of supplying a certain amount of electric current between the seed electrodes 12 and the copper electrode 56, and is turned on and off depending on a signal being applied from a control unit or a manipulation panel that is manually manipulated directly by a user.

The actuator 64 escalates the insulating substrate 11 up and down, and is configured to have a solenoid structure, a drive motor and a screw bar that are driven by an electric power applied from another power supply (not shown). When the drive motor is driven, the screw bar is made to rotate to thus escalate the insulating substrate up and down. Besides, a structure of escalating the insulating substrate 11 up and down such as a power cylinder structure may be applied for the actuator.

The function of the electroplating apparatus according to the embodiment of the present invention having the above-described configuration will be described below.

An insulating substrate 11 on which seed electrodes 12 are formed is placed on top of a water tank 50. Here, the water tank 50 is filled with a non-polar solvent 52, and an electrolyte layer 54 is formed on top of a non-polar solvent 52.

Under these conditions, when the actuator 64 is made to operate, the insulating substrate 11 descends and is inserted into the inside of the water tank 50, to then contact the electrolyte layer 54. When electric current is applied between the copper electrode 56 and the seed electrodes 12 from the power supply 62, a copper film is locally formed on the surface of the respective seed electrodes 12 only at a portion where the electrolyte layer 54 is positioned. That is, when electric current is applied between the copper electrode 56 and the seed electrodes 12 from the power supply 62, metal ions of the copper electrode 56 are electrodeposited on the surface of the respective seed electrodes 12, to thereby form the copper film on the surface of the respective seed electrodes 12.

In addition, when the insulating substrate 11 descends at a constant speed, a copper film having a uniform thickness is formed on the surface of the respective seed electrodes 12 over the whole insulating substrate 11.

Likewise, since a copper film is formed locally only at a portion where the electrolyte layer 54 exists, in the electroplating apparatus according to the embodiment, thickness of the copper film may be uniformly formed all over the entire surface of the large substrate, identically with the case that a copper film is formed on a small substrate.

When the copper plating process of making an insulating substrate move downwards and performing the plating operation is executed once, copper (Cu) grain that is relatively uniform in size can be produced with 2000-3000 Å in thickness on a large-sized substrate. Here, the electrodeposited copper film of 2000-3000 Å thick also provides an effect of lowering resistance of the metal electrode that is the cathode. In addition, in the case of thickening thickness of the copper film, the insulating substrate is made to repetitively descend in the inside of the water tank to thus electrodeposite the copper film on the insulating substrate.

In addition, in the present invention, a descending speed of an insulating substrate and an electric current density may significantly influence upon a copper (Cu) electrodeposition speed, a copper (Cu) grain size, and an electrodeposition shape. That is, when the electric current density becomes high above a certain value, electrodeposition is performed in a dendroid form. In this case, even if the descending speed of the insulating substrate becomes a certain value or less, electrodeposition is performed in a dendroid form.

In addition, if the descending speed is too slow, an electrodeposited copper film becomes thick and thus resistance of the metal electrode becomes lowered. Accordingly, a phenomenon of instantaneously increasing the electric current density appears. Thus, the present invention can form the copper film at the electric current density and the descending speed that do not cause the dendroid growth to occur, to thereby obtain a uniform copper film. To this end, a scanning operation is executed first at a high electric current density, to thus make nucleation, and then the insulating substrate is made to repeatedly descend at a low electric current density, to thereby avoid a dendroid phenomenon and fill copper into a trench.

In addition, if the electric current density becomes a certain value or less, or the descending speed is too fast, it is difficult to attain nucleation. Accordingly, grain size becomes large and surface of the copper film becomes rough.

In the present invention, all metals including copper and metal alloys thereof can be used as electrodeposition metal.

In this manner, it is possible to form a thin copper film, and perform an electroplating by making the whole insulating substrate dip into an electrolyte, to thus form a uniform copper film or fill copper into a trench or hole.

FIG. 4 is a perspective view showing an electroplating apparatus according to another embodiment of the present invention.

Referring to FIG. 4, the electroplating apparatus according to the embodiment of the present invention includes: a water tank 50 that is filled with a first non-polar solvent 70 having a higher specific gravity than an electrolyte and a second non-polar solvent 72 having a lower specific gravity than the electrolyte in which an electrolyte layer 54 is formed between the first and second non-polar solvents 70 and 72; a copper electrode 56 that is installed at an upper-inner end of the water tank 50; an insulating substrate 11 that is disposed to move up and down in the water tank 50 and on which seed electrodes 12 are formed, to thus form a copper film thereon, in which the insulating substrate 11 is withdrawn from the inside of the water tank 50 to the outside of the water tank 50; an actuator 64 that escalates the insulating substrate 11 up and down; and a power supply 62 that applies electric current between the copper electrode 56 and each of the seed electrodes 12.

The upper surface of the water tank 50 is opened to thereby make the insulating substrate 11 inserted into and withdrawn from the water tank 50 vertically through the opened upper surface. In addition, the water tank 50 is enough high to make the insulating substrate 11 inserted entirely into the water tank 50. Further, the water tank 50 is enough wide to make the insulating substrate 11 inserted entirely into the water tank 50. However, if the water tank 50 has a narrow width, the electrolyte or non-polar solvents can be saved to thus prevent waste thereof.

A solvent whose specific gravity is higher than that of an electrolyte and that is not mixed with the electrolyte is used as the first non-polar solvent 70 in order that the electrolyte may be disposed on the upper surface of the first non-polar solvent 70.

In addition, a solvent whose specific gravity is lower than that of an electrolyte and that is not mixed with the electrolyte is used as the second non-polar solvent 72 in order that the electrolyte may be disposed on the lower surface of the second non-polar solvent 72.

Thus, an electrolyte layer 54 of a certain thickness is formed between the first and second non-polar solvents 70 and 72.

A copper sulfate aqueous solution may be preferably used as an electrolyte. In addition, chloroform whose specific gravity is one or more may be preferably used as the first non-polar solvent 70, and hexane whose specific gravity is one or less may be preferably used as the second non-polar solvent 72.

In the copper electroplating apparatus according to the embodiment of the present invention having the above-described structure, when the insulating substrate 11 is made to move up by the actuator 64 and thus the insulating substrate 11 is withdrawn from the water tank 50, a copper film is formed on the seed electrodes 12 of the insulating substrate 11.

The function of the electroplating apparatus having the above-described configuration according to the embodiment of the present invention will follow. An insulating substrate 11 on which seed electrodes 12 have been formed is disposed in the inside of the water tank 50. Here, an electrolyte layer 54 is formed between the first and second non-polar solvents 70 and 72, in the water tank 50.

Under these conditions, when the actuator 64 is made to operate, the insulating substrate 11 is withdrawn from the inside of the water tank 50 to the outside of the water tank 50 at constant speed. In addition, when electric current is applied between the copper electrode 56 and the seed electrodes 12 from the power supply 62, a copper film is locally formed on the surface of the respective seed electrodes 12 only at a portion where the electrolyte layer 54 is positioned.

That is, when electric current is applied between the copper electrode 56 and the seed electrodes 12 from the power supply 62, metal ions of the copper electrode 56 are electrodeposited on the surface of the respective seed electrodes 12, to thereby form the copper film on the surface of the respective seed electrodes 12.

In addition, when the insulating substrate 11 ascends at a constant speed and thus is completely withdrawn from the inside of the water tank 50 to the outside of the water tank 50, a copper film having a uniform thickness is formed on the surface of the respective seed electrodes 12 over the whole insulating substrate 11.

Likewise, since a copper film is formed locally only at a portion where the electrolyte layer 54 exists, in the electroplating apparatus according to the embodiment, thickness of the copper film may be uniformly formed all over the entire surface of the large substrate, identically with the case that a copper film is formed on a small substrate.

FIG. 5 is a plan view illustrating an array substrate of a liquid crystal display device according to the present invention.

The liquid crystal display device includes an array substrate, a color filter substrate, and a liquid crystal layer formed between the array substrate and the color filter substrate, to thus display images thereon.

Referring to FIG. 5, the array substrate includes a number of gate lines (GLs) extended in a first direction (D1) and a number of data lines (DLs) extended in a second direction (D2) orthogonal to the first direction (D1). A number of pixel regions (pixel electrodes) 23 are defined by a number of the gate lines (GLs) that are formed simultaneously with a number of gate electrodes 14, or a number of the data lines (DLs) that are formed in a direction orthogonal to the number of the gate lines (GLs) and connected to a source electrode (S), respectively.

In addition, the array substrate includes a number of thin film transistors (TFTs) in which each thin film transistor (TFT) includes the gate electrode 14 branched from the gate line (GL), a source electrode (S) branched from the data line (DL), and a drain electrode (D) that is electrically connected in correspondence to the pixel electrode 23.

A process of manufacturing a thin film transistor (TFT) according to an embodiment of the present invention in which the thin film transistor (TFT) is included in the array substrate will be described with reference to FIGS. 6 through 21.

As shown in FIG. 6, a base metal film 120 that is formed of a first adhesive layer 120 a and a first electrode layer 120 b that are respectively formed of a conductor, for example, one of Ni, MoW, and Al through a sputtering or thin film deposition method is formed on a transparent insulating substrate 11, for example, a glass substrate.

Here, the first adhesive layer 120 a is formed into a thickness of 500 Å using nickel (Ni) for example, and the first electrode layer 120 b is formed into a thickness of 2000 Å using molybdenum-tungsten (MoW) for example.

Then, after having formed a photoresist although it is not shown in FIG. 7, the base metal film 120 is patterned using a gate mask, to thereby form a seed electrode 12 in correspondence to the gate electrode of a shape shown in FIG. 7.

By doing so, the seed electrode 12 is completely patterned. Upon completion of the seed electrode formation, for example, a 1.5 micrometer-thick insulating film 13 is deposited using silicon oxide or silicon nitride by a plasma enhanced chemical vapor deposition (PECVD) method as shown in FIG. 8.

Thereafter, a photoresist layer 15 is coated on top of the insulating film 13, as shown in FIG. 9. Then, a back exposure process is performed. Then, the photoresist layer 15 is exposed and developed by the back exposure without using a mask and then the negative type photoresist layer 15 that is not exposed by the seed electrode 12 is removed. As a result, the remaining etching mask 15 a is self-aligned as shown in FIG. 10, and a recess pattern is formed in correspondence to a gate pattern. Here, the insulation film 13 corresponding to the recess pattern corresponding to the gate pattern is reactive-ion-etched using hydrofluoride (HF) through the remaining etching mask 15 a. Then, as shown in FIG. 11, a trench type guide portion 16 is formed on the insulating substrate 11 and thus a trench type contact window is formed to make the upper portion of the seed electrode 12 exposed. Thereafter, the etching mask 15 a is removed.

Subsequently, copper is selectively electrodeposited with one or two micrometers thick on the exposed seed electrode 12 by an electroplating method using the trench type guide portion 16. As a result, copper is not electrodeposited on the trench type guide portion 16 but is electrodeposited on only the exposed upper trench of the exposed seed electrode 12 to thus selectively form a copper film 37 that is a gate electrode. In other words, the seed electrode 12 is set as a cathode and the copper is set as an anode, to then carry out an electroplating process. Accordingly, the copper film 37 is selectively formed.

In the present invention, the copper film 37 is formed in a scanning manner by the electroplating apparatus that are shown in FIG. 3 or 4, as a copper plating process of forming the copper film 37 that is a copper gate electrode.

In addition, in the case that thickness of the copper film 37 is thinner than a set value, the insulating substrate is dipped into the electrolyte tub and then the electroplating process is executed once again, to thereby form the a copper gate electrode 14.

In addition, as shown in FIG. 12, in order to achieve planarization of the copper gate electrode 14, a planarization process such as a CMP (Chemo-Mechanical Polishing) process or a grinding process is executed considering that the copper gate electrode 14 is formed on the trench type guide portion 16, to thus execute planarization of the copper wires and the trench type guide portion 16.

Here, it is necessary to make a polishing unit move in a random direction on a large-area substrate, to thus planarize a copper gate that has been excessively charged or filled. In addition, the copper gate is polished with only a fine abrasive agent without using a copper etching solution, to thus planarize the excessively charged or filled copper gate.

In this case, wires for gate lines (GLs) that are connected with the gate electrode 14 and are used to apply a gate signal to a thin film transistor (TFT) are preferably simultaneously formed. Here, data lines (DLs) that are connected to a source electrode (S) are also preferably formed in the same process and material as those of the gate lines (GLs).

Then, as shown in FIG. 13, a gate insulation film 17 is deposited by a thickness of 1000 Å on the gate electrode 14 and the trench type guide portion 16, by a PECVD (Plasma-Enhanced Chemical Vapor Deposition) method, for example. A silicon oxide film or silicon nitride film can be used as the gate insulation film 17.

Then, as shown in FIG. 14, an amorphous silicon layer 18 is deposited on the gate insulation film 17 by for example, a CVD (Chemical Vapor Deposition) method. In order to form a source region and a drain region during deposition of the amorphous silicon layer 18, an in-situ doping process can be simultaneously done.

In the case of forming the polysilicon thin film transistor (TFT), the in-situ doping process is not generally performed as will be described later. In the case that crystallization is performed using laser, a crystallization process is performed in front of or at the back of a protective oxide film. In the case of using a non-laser method, the crystallization process may vary depending on the applied method. In this embodiment, a metal induced lateral crystallization (MILC) method is applied for crystallization of the amorphous silicon layer as an example.

After the amorphous silicon layer 18 has been deposited, a photoresist mask 19 is formed as shown in FIG. 15, in order to form a metal induced film to induce crystallization of the amorphous silicon layer 18 by a lift-off method. Then, a nickel pattern layer 20 that is a metal induced film for the metal induced lateral crystallization MILC is formed on the photoresist mask 19 to then be removed as shown in FIG. 16. Here, Pd, Ti, Ag, Au, Al, Sn, Sb, Cu, Co, Cr, Mo, Tr, Ru, Rh, Cd, Pt, etc., may be used as materials of the crystallization metal induced film, in addition to nickel.

After the nickel pattern layer 20 has been formed, the amorphous silicon layer 18 is crystallized by a MILC (metal induced lateral crystallization) low-temperature heat treatment. Then, the nickel pattern layer 20 is removed to thereby form a crystallizing silicon layer 18 a as shown in FIG. 17.

Here, a technology of metal-induced-lateral-crystallizing the amorphous silicon layer by the MILC heat treatment is disclosed in Korean Patent Laid-open Publication No. 10-2009-42122 that was filed earlier by the same inventor as that of the present invention. Accordingly, the detailed description thereof will be omitted.

After the MILC heat treatment has been performed, the amorphous silicon layer has been completely crystallized, and then the polysilicon layer 18 a has been formed, a protective oxide film 21 is deposited with a thickness of 3000 on the polysilicon layer 18 a as shown in FIG. 19. In addition, a photoresist is coated on the protective oxide film 21 to thereby form a photoresist layer 22 as shown in FIG. 19.

Then, as shown in FIG. 19, the photoresist layer 22 is exposed and developed by back exposure without using a mask. Then, the unexposed photoresist layer 22 is removed. Then, when the protective oxide film 21 is etched using a remaining etching mask not shown, an ion implantation shielding mask 21 a is formed as shown in FIG. 20.

Using the ion implantation shielding mask 21 a, a source region and a drain region are formed by a dopant ion mass doping (IMD) process, and the ion mass doped dopant is activated by a heat treatment process.

Referring to FIG. 21, etching masks (not shown) are formed on the activated source electrode (S) and the activated drain electrode (D), to then form a channel layer (C) by an etching process. Then, a protective film 22 made of an inorganic insulation film is formed on the channel layer (C) as well as the source electrode (S) and the drain electrode (D). Then, a contact hole that exposes the drain electrode (D) through the protective film 22 is formed. Then, a pixel electrode 23 made of ITO (indium tin oxide) or IZO (indium zinc oxide) is formed on the protective film 22, to accordingly complete manufacturing of an array substrate.

In the above description of the embodiment of the present invention, the case that the gate lines have been formed in the same manner and material as those of the gate electrode has been described as an example. However, the data lines that are connected to the source electrode can be formed in he same manner and material as those of the gate lines.

The above-described process of manufacturing the copper bottom gate thin film transistor may employ the other crystallization methods instead of the above-described MILC method, on the substrate where the planarized and thick gate copper wires are achieved. It is also possible to modify part of the TFT manufacturing process.

As described above, copper with a low resistance value that is suitable for a large display is formed into a thickness usable for a bottom gate according to an electroplating method, in the present invention, to thereby solve a step coverage problem without passing through a planarization process of copper that is used as a gate electrode.

In addition, since the present invention uses copper in a gate electrode, a source region and a drain region can be automatically aligned with respect to a gate by back exposure without using a separate mask, to thereby minimize an alignment error.

In the above embodiment of the present invention, the case that polysilicon has been used as an active area as an example, but it is possible to use amorphous silicon as the active area.

However, in this case, it is required to form a mask in the conventional well-known manner, instead of forming the ion implantation shielding mask using back exposure.

The present invention can be applied to a thin film transistor that is used for a display device such as an active-matrix liquid crystal display AMLCD) or an active-matrix organic light emitting diode AMOLED) display and a wiring method thereof.

As described above, the present invention has been described with respect to particularly preferred embodiments. However, the present invention is not limited to the above embodiments, and it is possible for one who has an ordinary skill in the art to make various modifications and variations, without departing off the spirit of the present invention. Thus, the protective scope of the present invention is not defined within the detailed description thereof but is defined by the claims to be described later and the technical spirit of the present invention. 

1. An electroplating apparatus comprising: a water tank that is filled with a non-polar solvent having a higher specific gravity than an electrolyte in which an electrolyte layer is formed on top of the non-polar solvent; a copper electrode that is installed at a portion where the electrolyte layer of the water tank is positioned; an actuator that escalates an insulating substrate up and down, the insulating substrate that is disposed to be inserted into and withdrawn from the water tank and on which seed electrodes are formed; and a power supply that applies electric current between the copper electrode and each of the seed electrodes.
 2. The electroplating apparatus according to claim 1, wherein chloroform whose specific gravity is 1.5 g/ml is used as the non-polar solvent.
 3. The electroplating apparatus according to claim 1, wherein a copper film is formed on the surface of each seed electrode, when the insulating substrate is inserted into the water tank.
 4. An electroplating apparatus comprising: a water tank that is filled with a first non-polar solvent having a higher specific gravity than an electrolyte and a second non-polar solvent having a lower specific gravity than the electrolyte in which an electrolyte layer is formed between the first and second non-polar solvents; a copper electrode that is installed at a portion where the electrolyte layer of the water tank is positioned; an actuator that escalates the insulating substrate up and down, the insulating substrate that is disposed to be inserted into and withdrawn from the water tank and on which seed electrodes are formed; and a power supply that applies electric current between the copper electrode and each of the seed electrodes.
 5. The electroplating apparatus according to claim 4, wherein chloroform is used as the first non-polar solvent, and hexane is used as the second non-polar solvent.
 6. The electroplating apparatus according to claim 4, wherein a copper film is formed on the surface of each seed electrode, when the insulating substrate is withdrawn from the water tank.
 7. An electroplating method comprising the steps of: filling a non-polar solvent whose specific gravity is higher than that of an electrolyte in a water tank and forming an electrolyte layer on top of the non-polar solvent; installing a copper electrode at a portion where the electrolyte layer of the water tank is positioned; inserting an insulating substrate on which seed electrodes are formed from the upper side of the water tank to the inside of the water tank at constant speed; and applying electric current between each of the seed electrodes and the copper electrode to thus sequentially form a copper film on the surface of each seed electrode that passes through the electrolyte layer.
 8. An electroplating method comprising the steps of: filling a first non-polar solvent whose specific gravity is higher than that of an electrolyte and a second non-polar solvent whose specific gravity is lower than that of the electrolyte in a water tank and forming an electrolyte layer between the first and second non-polar solvents; installing a copper electrode at a portion where the electrolyte layer of the water tank is positioned; withdrawing an insulating substrate on which seed electrodes are formed from the inside of the water tank to the upper side of the water tank at constant speed; and applying electric current between each of the seed electrodes and the copper electrode to thus sequentially form a copper film on the surface of each seed electrode that passes through the electrolyte layer. 